1

NIST TIME AND FREQUENCY BULLETIN 

NISTIR 6629-10

 NO. 550 OCTOBER 2003 

1. GENERAL BACKGROUND INFORMATION ............................................................................................... 2

2. TIME-SCALE INFORMATION ..................................................................................................................... 2

3. PHASE DEVIATIONS FOR WWVB AND LORAN-C ................................................................................... 4

4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB 

 PHASE PERTURBATIONS........................................................................................................................... 5

5. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS............................................................... 5

6. BIBLIOGRAPHY.............................................................................................................................................. 5

7. SPECIAL ANNOUNCEMENTS..................................................................................................................... 7

This bulletin is published monthly. Address correspondence to: 

Eyvon M. Petty, Editor 

Time and Frequency Division 

National Institute of Standards and Technology

325 Broadway 

Boulder, CO 8O3O5-3328 

(3O3) 497-3295

Email: pettye@boulder.nist.gov

NOTE TO SUBSCRIBERS: Please include your address label (or a copy) 

with any correspondence regarding this bulletin. 

U.S. DEPARTMENT OF COMMERCE, DONALD L. EVANS, Secretary

TECHNOLOGY ADMINISTRATION, Dr. Cheryl L. Shavers, Under Secretary of Commerce for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Dr. Arden L. Bement, Jr., Director
2 

1. GENERAL BACKGROUND INFORMATION

_______________________________________________________________________________________________________ 

ACRONYMS AND ABBREVIATIONS USED IN THIS BULLETIN

BIPM - Bureau International des Poids et Mesures 

Cs - Cesium standard 

GPS - Global Positioning System 

IERS - International Earth Rotation Service 

LORAN - Long Range Navigation 

MC - Master Clock 

MJD - Modified Julian Date 

NVLAP - National Voluntary Laboratory Accreditation Program 

NIST - National Institute of Standards and Technology 

NOAA - National Oceanic and Atmospheric Administration ns - nanosecond 

SI - International System of Units μs - microsecond 

TA - Atomic Time ms - millisecond 

TAI - International Atomic Time s - second 

USNO - United States Naval Observatory min - minute 

UTC - Coordinated Universal Time 

_______________________________________________________________________________________________________ 

 2. TIME-SCALE INFORMATION

 The values listed below are based on data from the IERS, the USNO, and NIST. The UTC(USNO,MC) - UTC(NIST) values are 

averaged measurements from all available common-view GPS satellites (see bibliography on page 5). UTC - UTC(NIST) data are 

on page 3.

 0000 HOURS COORDINATED UNIVERSAL TIME 

SEP 2003 MJD UT1-UTC(NIST) 

 (±5 ms) 

UTC(USNO,MC) - UTC(NIST) 

 (±20 ns) 

4 52886 -353 ms 0 ns 

11 52893 -352 ms -2 ns 

18 52900 -353 ms -3 ns 

25 52907 -354 ms 0 ns 

 

 The master clock pulses used by the WWV, WWVH, and WWVB time-code transmissions are referenced to the UTC(NIST) time 

scale. Occasionally, 1 s is added to the UTC time scale. This second is called a leap second. Its purpose is to keep the UTC time 

scale within ±0.9 s of the UT1 astronomical time scale, which changes slightly due to variations in the rate of rotation of the Earth. 

NOTE: NO leap second will be inserted at the end of December 2003.

 Positive leap seconds, beginning at 23 h 59 min 60 s UTC and ending at 0 h 0 min 0 s UTC, were inserted in the UTC 

timescale on 30 June 1972, 1981-1983, 1985, 1992, 1993, 1994, and 1997, and on 31 December 1972-1979, 1987, 1989, 

1990,1995, and 1998. There have been 22 leap seconds inserted in total. 

 The use of leap seconds ensures that UT1 - UTC will always be held within ±0.9 s. The current value of UT1 - UTC is called the 

DUT1 correction. DUT1 corrections are broadcast by WWV, WWVH, and WWVB and are printed below. These corrections may be 

added to received UTC time signals in order to obtain UT1. 

_______________________________________________________________________________________________________ 

 +0.1 s beginning 0000 UTC 19 October 2000 

 +0.0 s beginning 0000 UTC 01 March 2001 

DUT1 = UT1 - UTC = -0.1 s beginning 0000 UTC 04 October 2001 

 -0.2 s beginning 0000 UTC 14 February 2002 

 -0.3 s beginning 0000 UTC 24 October 2002 

 -0.4 s beginning 0000 UTC 03 April 2003 

 
3 

 

The deviation of UTC(NIST) from UTC has been within +/–100 ns since July 6, 1994. The table below shows values of 

UTC - UTC(NIST) as supplied by the BIPM in their Circular T publication for the most recent 310-day period in which data 

are available. Data are given at ten day intervals. Five day interval data are available in Circular T. 

0000 Hours Coordinated Universal Time 

DATE MJD UTC-UTC(NIST) ns 

Aug. 28, 2003 52879 7.7 

Aug. 18, 2003 52869 8.0 

Aug. 8, 2003 52859 10.2 

Jul. 29, 2003 52849 10.7 

Jul. 19, 2003 52839 12.7 

Jul. 9, 2003 52829 12.6 

Jun. 29, 2003 52819 9.2 

Jun. 19, 2003 52809 7.5 

Jun. 9, 2003 52799 3.8 

May 30, 2003 52789 0.6 

May 20, 2003 52779 4.0 

May 10, 2003 52769 10.4 

Apr. 30, 2003 52759 8.9 

Apr. 20, 2003 52749 10.7 

Apr. 10, 2003 52739 10.9 

Mar. 31, 2003 52729 11 

Mar. 21, 2003 52719 12 

Mar. 11, 2003 52709 11 

Mar. 1, 2003 52699 7 

Feb. 19, 2003 52689 8 

Feb. 9, 2003 52679 7 

Jan. 30, 2003 52669 2 

Jan. 20, 2003 52659 -1 

Jan. 10, 2003 52649 -5 

Dec. 31, 2002 52639 -2 

Dec. 21, 2002 52629 -3 

Dec. 11, 2002 52619 -4 

Dec. 1, 2002 52609 -3 

Nov. 22, 2002 52599 2 

Nov. 12, 2002 52589 3 

Nov. 2, 2002 52579 4 

 

 
4 

3. PHASE DEVIATIONS FOR WWVB AND LORAN-C

WWVB - The values shown for WWVB are the time differences between the time markers of the UTC(NIST) time scale 

and the first positive-going zero voltage crossover measured at the transmitting antenna. The uncertainty of 

the individual measurements is ±0.5 μs. The values listed are for 1300 UTC. 

LORAN-C - The values shown for Loran-C represent the daily accumulated phase shift (in ns). The phase shift is 

measured by comparing the output of a Loran receiver to the UTC(NIST) time scale for a period of 24 h. If data 

were not recorded on a particular day, the symbol (-) is printed. The stations monitored are Baudette, ND 

(8970-Y) and Fallon, NV (9940). The monitoring is done from the NIST laboratories in Boulder, Colorado. 

Note: The values shown for Loran-C are in nanoseconds. 

 

 UTC(NIST)-WWVB (60 kHz) UTC(NIST) - LORAN PHASE (ns)

 

 ANTENNA PHASE LORAN-C (BAUDETTE) LORAN-C (FALLON) 

DATE MJD (μs) (8970) (9940) 

09/01/03 52883 5.67 +34 -170 

09/02/03 52884 5.68 -62 -397 

09/03/03 52885 5.69 -18 +151 

09/04/03 52886 5.67 +42 -123 

09/05/03 52887 5.67 -10 +281 

 

09/06/03 52888 5.68 -31 -77 

09/07/03 52889 5.68 -17 -72 

09/08/03 52890 5.68 +30 +325 

09/09/03 52891 5.65 -84 +277 

09/10/03 52892 5.68 +8 +46 

 

09/11/03 52893 5.68 -34 -469 

09/12/03 52894 5.67 +14 -295 

09/13/03 52895 5.66 -39 -52 

09/14/03 52896 5.65 +11 +129 

09/15/03 52897 5.64 +59 -453 

 

09/16/03 52898 5.67 -9 -390 

09/17/03 52899 5.66 -70 -13 

09/18/03 52900 5.66 +2 +104 

09/19/03 52901 5.66 -8 -334 

09/20/03 52902 5.66 +24 +172 

 

09/21/03 52903 5.65 -39 +17 

09/22/03 52904 5.65 -10 +256 

09/23/03 52905 5.65 +27 -158 

09/24/03 52906 5.64 -75 +64 

09/25/03 52907 5.64 +36 +269 

 

09/26/03 52908 5.65 -50 +239 

09/27/03 52909 5.65 +2 -295 

09/28/03 52910 5.65 +23 -322 

09/29/03 52911 5.64 -66 +15 

09/30/03 52912 5.64 +14 +227 

 
5 

 

4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS

OUTAGES OF 5 MINUTES OR MORE 

WWVB 60 kHz

 

PHASE PERTURBATIONS 

2 ms 

Station SEP 

2003 

 MJD Began 

UTC 

Ended 

UTC 

Freq. SEP 

2003 

MJD Began 

 UTC 

End 

UTC 

WWVB 9-19-03 52901 0408 0428 60 kHz 

WWVB 9-19-03 52901 0014 0048 60 kHz 

WWVB 9-18-03 52900 1221 1312 60 kHz 

WWVB 9-15-03 52897 0825 0930 60 kHz 

WWV 

WWVH 

5. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS 

 Primary frequency standards developed and operated by NIST are used to provide accuracy (rate) input to the BIPM. NIST-7 was 

the U.S. primary standard from 1994 to 1999, when it was replaced by NIST-F1, a cold atom cesium fountain frequency standard. 

The uncertainty of NIST-F1 is currently 1 part in 1015. 

 The AT1 scale is run in real-time using data from an ensemble of cesium standards and hydrogen masers. It is a free-running scale 

whose frequency is maintained as nearly constant as possible by choosing the optimum weight for each clock that contributes to the 

computation. 

 UTC(NIST) is generated as an offset from our real-time scale AT1. It is steered in frequency towards UTC using data published by 

the BIPM in its Circular T. Changes in the steering frequency will be made, if necessary, at 0000 UTC on the first day of the month, 

and occasionally at mid-month. A change in frequency is limited to no more than ± 2 ns/day. The frequency of UTC(NIST) is kept as 

stable as possible at other times. 

 UTC is generated at the BIPM using a post-processed time-scale algorithm and is not available in real-time. The parameters that 

we use to generate UTC(NIST) in real-time are therefore based on an extrapolation of UTC from the most recent data available. 

 

6. BIBLIOGRAPHY 

Allan, D.W.; Hellwig, H.; and Glaze, D.J., "An accuracy algorithm for an atomic time scale," Metrologia, Vol.11, No.3, pp.133-138 

(1975). 

Allan, D.W.; Davis, D.D.; Weiss, M.A.; Clements, A.; Guinot, B.; Granveaud, M.; Dorenwendt, K.; Fischer, B.; Hetzel, P.; Aoki, S.; 

Fujimoto, M.; Charron, L.; and Ashby, N., “Accuracy of International Time and Frequency Comparisons Via Global Positioning System 

Satellites in Common-view,” IEEE Transactions on Instrumentation and Measurement, Vol. IM-34, pp.118-125, 1985. 

Jefferts, S.R.; Shirley, J.; Parker, T.E.; Heavner, T.P.; Meekhof, D.M.; Nelson, C., Levi, F.; Costanza, G.; De Marchi, A.; 

Drullinger, R.; Hollberg, L.; Lee, W.D.; and Walls, F.L., “Accuracy evaluation of NIST-F1,” Metrologia, Vol. 39, pp. 321-336, 

(2002). 

Lewandowski, W. and Thomas, C.; “GPS Time transfer,” Proceedings of the IEEE, Vol. 79, pp. 991-1000, 1991. 

Shirley, J.H.; Lee, W.D.; Drullinger, R.E.; “Accuracy evaluation of the primary frequency standard NIST-7,” Metrologia, Vol. 38, pp. 

427-458, (2001). 

Weiss, M.A.; Allan, D.W.; “An NBS Calibration Procedure for Providing Time and Frequency at a Remote Site by Weighting and 

Smoothing of GPS Common View Data,” IEEE Transactions on Instrumentation and Measurement, Vol. IM-36, pp. 572-578, 1987. 
 6 

Table 7.1 lists parameters that are used to define UTC(NIST) with respect to our real-time scale AT1. To find the 

value of UTC(NIST) - AT1 at any time T (expressed as a Modified Julian Day, including a fraction if needed), the 

appropriate equation to use is the one for which the desired T is greater than or equal to the entry in the T0

 column 

and less than the entry in the last column. The values of xls, x, and y for that month are then used in the equation 

below to find the desired value. The parameters x and y represent the offset in time and in frequency, respectively, 

between UTC(NIST) and AT1; the parameter xls is the number of leap seconds applied to both UTC(NIST) and UTC 

as specified by the IERS. Leap seconds are not applied to AT1. 

Table 7.1 

UTC(NIST) - AT1 = xls + x + y*(T −T0

) 

Month xls

(s) 

x 

(ns) 

y 

(ns/d) 

 T0

(MJD) 

Valid until 0000 on: 

(MJD) 

 Nov 03 -32 -256336.95 -39.5* 52944 52974* 

 Oct 03 -32 -255112.45 -39.5 52913 52944 

 

 Sep 03 -32 -253927.745 -39.5 52883 52913 

 Aug 03 -32 -252702.95 -39.5 52852 52883 

 Jul 03 -32 -252228.95 -39.5 52840 52852 

 Jul 03 -32 -251473.7 -39.75 52821 52840† 

 Jun 03 -32 -251076.2 -39.75 52811 52821 

 Jun 03 -32 -250276.2 -40.0 52791 52811† 

 May 03 -32 -249652.2 -39.0 52775 52791 

 May 03 -32 -249052.2 -40.0 52760 52775† 

 Apr 03 -32 -248495.7 -39.75 52746 52760 

 Apr 03 -32 -247855.7 -40.0 52730 52746† 

 Mar 03 -32 -247415.7 -40.0 52719 52730 

 Mar 03 -32 -246607.7 -40.4 52699 52719† 

 Feb 03 -32 -246284.9 -40.35 52691 52699 

 Feb 03 -32 -245474.9 -40.5 52671 52691† 

 Jan 03 -32 -244906.5 -40.6 52657 52671 

 Jan 03 -32 -244218.0 -40.5 52640 52657† 

 Dec 02 -32 -243813.0 -40.5 52630 52640 

 Dec 02 -32 -242964.6 -40.4 52609 52630† 

 Nov 02 -32 -242399.0 -40.4 52595 52609 

 Nov 02 -32 -241751.0 -40.5 52579 52595† 

 Oct 02 -32 -240495.5 -40.5 52548 52579 

 Sep 02 -32 -240252.5 -40.5 52542 52548 

 Sep 02 -32 -239274.5 -40.75 52518 52542† 

† Rate change in mid-month 

†† Rate change one day early 

*Provisional value 
7

IMPORTANT NOTICE!

Effective January 1, 2004, NIST will discontinue sending the bulletin by mail.

The Time and Frequency Bulletin data are now online at

www.boulder.nist.gov/timefreq/pubs/bulletin/timescaleindex.htm

7. SPECIAL ANNOUNCEMENTS 

NOTICE TO DISCONTINUE INVOLVEMENT WITH GOES TIME CODE SERVICE

NIST has announced that it will discontinue its involvement with the time code broadcast from the GOES WEST and 

GOES EAST satellites operated by the National Oceanic and Atmosphere Administration (NOAA) on January 1, 2005. 

This decision has been jointly made by NIST and NOAA in response to the fact that nearly all users requiring time more 

accurate than 1 millisecond now use the Global Positioning System (GPS), and as a result, commercial sources for 

GOES timing receivers no longer exist.

NOAA is expected to continue to provide a GOES time code indefinitely after January 1, 2005, and existing receivers 

should be able to continue to receive and decode the time signal. However, the time code will no longer be controlled 

and checked by NIST, and the received time is expected to be less accurate when NIST discontinues its involvement. 

The GOES satellites currently broadcast continuously updated position information in addition to the time, so that GOES 

receivers can automatically correct for path delay changes caused by satellite motion. This allows the current system to 

have a time uncertainty of less than 100 microseconds. NOAA is expected to continuously broadcast a fixed position 

from the satellites, which could increase the time uncertainty to 1 millisecond or more. 

The GOES time broadcasts began in 1974 and have served many applications and thousands of users. NIST will 

continue to control and monitor the time code through January 1, 2005 to allow users who require a high accuracy 

signal sufficient time to replace their existing receivers. If you have additional questions, please contact Michael 

Lombardi, 303-497-3212, or email lombardi@boulder.nist.gov.